1. Field of the Invention
The present invention relates to a private branch radio communication system and, more particularly, to a private branch radio communication system using optical fibers.
2. Description of the Related Art
On sites such as power plants or substations, large numbers of personnel may be engaged in jobs related to each other, but often doing so in widely separated locations throughout the site. For this reason, a radio communication system is generally used to enable personnel to communicate with each other, with each worker carrying a portable radio transceiver while doing his job, and exchanging information with other personnel, as and when required.
This type of radio communication system utilizes a relatively weak radio wave, this being because if a strong radio wave were to be used, it might interfere with the operation of various electronic devices located on the same premises.
If radio communication is to be performed in a building, especially in a so-called intelligent building in which various systems, such as the air conditioning system, for example, are computer-controlled, a very weak radio wave, e.g., a radio wave having a field intensity of 500 .mu.V/m or less which is measured at, for example, a position 3 m away from a radio wave source, should preferably be used in order to prevent erroneous operation of various electronic devices in the building, as a result of radio interference. However, in buildings, the transmitting of radio waves tends to be hindered by walls, pillars, and the like. Therefore, when a weak radio wave is, for the aforestated reasons, used for communication within a building, satisfactory communication from the ground floor to the uppermost floor cannot be achieved. For this reason, radio communication using a weak radio wave can be employed only for private branch communication within a confined area, e.g., within one floor of a building, but not throughout all floors of the building. As a result, the range through which personnel can move and remain in communication is undesirably limited.